This invention relates to conduit systems of the type described in U.S. Pat. No. 4,625,746, which have a frangible connector, and which also have two automatic sealing mechanisms for blocking the flow of fluid out of the ruptured ends of the conduit should the connector become broken.
As described in U.S. Pat. No. 4,625,746, it is often important to prevent leakage of flammable or noxious fluids from a conduit after the conduit has been ruptured. For example, fuel spillage from an aircraft fuel line after a crash can result in an explosion or severe fire. In order to avoid such spillage, frangible connectors have been developed with the object of controlling the location in the fuel line at which a break will take place, and by providing a valve mechanism which acts automatically to seal off the spillage of fuel out of the fuel line at the ruptured ends of the fuel line adjacent to the frangible connector as quickly as possible.
In the prior art assemblies, to accomplish the objectives described in the preceding paragraph, the fuel line or other conduit is typically divided into two sections which are joined together by one or more frangible connectors. The frangible connector has a relatively weak linkage holding it together so that under the stress of a crash, or other accident, a break will occur at the connector before anywhere else in the conduit. A valve mechanism is provided in the conduit sections on either or each side of the frangible connector which acts automatically to stop the spillage of fluid when the connector is broken. It is important, of course, that the valve mechanism be fast operating, reliable and, especially for aerospace applications, be as small and as light-weight as possible.
One type of valve mechanism for a frangible connector is described in U.S. Pat. No. 4,625,746 referred to above. In the mechanism of that patent, two butterfly valves are mounted in respective fluid-carrying conduit sections in the vicinity of a frangible connector which connects the two conduit sections together in a coaxially aligned relationship. Each valve in the mechanism described in the patent comprises a sealing disc which is pivotally mounted in its conduit section, and the mechanism includes spring means in each of the conduit sections which biases the corresponding disc about its rotational axis toward a closed position sealing the corresponding section. In the mechanism described in the patent, the two discs are positioned so that they pivot on mutually intersecting arcs with each disc normally abutting against the other in an open position, thereby preventing each other from closing. When the frangible connector is broken, however, and the two conduit sections become separated, and the discs are released, and they are pivoted by their respective springs to closed positions and latched to seal off the ruptured ends of the corresponding conduit sections.
The sealing mechanism of the present invention is generally similar to the mechanism described in U.S. Pat. No. 4,625,746. Specifically, the mechanism of the present invention also includes a pair of conduit sections which are held together in coaxial relationship by frangible connectors, and which further includes a butterfly valve pivotally mounted in each of the conduit sections, with the two valves being spring biased to a closed position and latched when the conduit sections become separated.
However, in the mechanism of the present invention the two butterfly valves do not overlap during normal flow of fluid through the conduit, but are held in their open position by a separate pivotally mounted flat spacer. The spacer and the two butterfly valves have a uniplanar relationship, and form a flat thin assembly during normal flow of fluid through the conduit. The resulting elimination of the overlapping relationship of the two butterfly valves as in U.S. Pat. No. 4,652,746 minimizes turbulence in the fluid flowing through the conduit, and accordingly reduces pressure drop/flow rate in the mechanism of the invention during normal operation.
Accordingly, an objective of the present invention is to provide an improved frangible sealing mechanism which includes a pair of conduit sections, each containing a spring biased butterfly valve, and which exhibits improved pressure drop/flow rate performance as compared with the prior art mechanisms of the same general type.
Another objective of the invention is to provide such an improved frangible valve sealing mechanism in which the distance between the pivotal axes of the two butterfly valves in the two conduit sections may be increased as compared with the maximum possible distance in the prior art mechanisms. This ability to increase the distance between the valve's pivotal axes is an advantage when dual frangible fuse planes must be incorporated into the design to comply with specification requirements, as is often the case.
One major area of concern in breakaway valve operation is the sticking potential of the seal on the shutoff valve. After several years of exposure to aircraft fuels, many seal compounds swell and cause high friction loads on the shutoff valves as they attempt to rotate to their closed positions after the conduit sections become separated. Because the closure of the valves is caused solely by preloaded springs, high friction loads can prevent the valves from closing, resulting in an open flow passage from the fuel system at a time when it is essential that the fuel be cut off.
The mechanism of the invention, in one of its embodiments, uses a pressure energized seal which inflates and improves sealing of the valve after it has been closed. This permits interference and friction during initial closure to be reduced with improved sealing to occur when a pressure differential across the valve is encountered. The pressure energized seal requires an upstream versus downstream pressure differential to inflate and seal. Such pressure differential does not occur until the valve is closed after separation of the two conduit sections because under normal fluid flow through the conduit both sides of the seal are equally pressurized when the valve is open. Accordingly, the pressure energized seal provides reduced friction during closure because (a) it is not energized until the valve is closed, and (b) it is made of non-elastomer material which does not swell when immersed in aircraft fuel. Pressure energized seals such as those described, for example, in U.S. Pat. Nos. 4,836,499; 4,176,675; 4,254,936; and 4,540,457, may be adapted for use in the mechanism of the invention.
The foregoing and other objects and features of the invention will become apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.